Faced with a countersuit, three Sierra Club board candidates have dropped a lawsuit that contended the leaders of the San Francisco-based organization are attempting to manipulate the upcoming board of directors election.

The move is the latest action in a controversy over immigration policy that Sierra Club leaders say threatens to sunder the venerable organization --

at 750,000 members, the biggest environmental group in the country.

The battle has been brewing since the 1990s, with the latest skirmish centering on the five open seats on the club's 15-person board of directors. The election will be determined by mail-in ballots from March 1 to April 15.

The three candidates favor tougher U.S. immigration quotas, contending population growth -- which is largely fueled by immigration -- is the greatest environmental problem facing the country.

Sierra Club President Larry Fahn, Executive Director Carl Pope and most of the club's board favor a neutral position on immigration, arguing that a stance favoring greater strictures would alienate many of the group's traditional allies.

The plaintiffs sought an injunction delaying the elections, claiming that Sierra Club officials were using club resources illegally to promote candidates chosen by a nominating committee over petition candidates -- including Lamm, Morris and Pimentel, who had each gathered about 400 signatures to get their names on the ballot.

Club leaders lambasted the lawsuit, claiming it was a calculated attempt to keep members from being informed about the election and the true platforms of the candidates. "This was a case of muzzling free speech," Pope said. "When so advised, the plaintiffs dropped their lawsuit, and we are glad they have done so."

James Turken, a lawyer for the plaintiffs, said his clients withdrew their suit "when they were informed that the club was going to file a countersuit asking for legal fees if our suit was unsuccessful. That could run into six figures. My clients are either acting or retired university professors. That information had a chilling effect on them."

Turken said the basis for the Sierra Club suit is a state law that allows for redress of legal fees if a suit "arguably infringes on First Amendment free speech. We don't think our suit does that, but my clients aren't in a financial position (to risk losing)."

Club attorneys said it was obvious the suit had little merit, and that it may have been a calculated effort to confound the organization's membership. "It was simply an attempt to keep the Sierra Club leadership quiet and members uninformed," said Thomas R. Burke, an attorney representing the club.